To deal with endianness issues in C, we need to clarify platform differences and take corresponding conversion measures. 1. To determine the system byte order, you can use simple functions to detect whether the current system is a little-endian; 2. When manually exchanging byte order, general conversion can be achieved through bit operations, but standard APIs such as ntohl() and htonl() are recommended; 3. Use cross-platform libraries such as Boost or absl to provide conversion interfaces, or encapsulate macros that are adapted to different architectures by themselves; 4. When processing structures or buffers, you should read and convert fields by field to avoid direct reinterpret_cast structure pointer to ensure data correctness and code portability.

The key to dealing with endianness in C is that you have a clear understanding of how data is stored and transmitted. Different hardware architectures may adopt different endian orders, such as x86 is little-endian, while some network protocols or embedded systems use big-endian. If you need to read and write binary data across platforms, communicate networks or parse file formats, you have to face this problem.

Determine the byte order of the current system

To handle endianness, you must first know which platform your program runs on. It can be detected by a simple trick:

 bool is_little_endian() {
    int num = 1;
    return *(char*)&num == 1;
}

This function takes advantage of the storage of integer variables in memory. Return true if the lowest address stores the low byte (that is, the little endian). Otherwise it's big end.

Once you master this, you can decide whether you need to do endian conversion based on the system type.

Manually swap byte order

When you know clearly that a certain data is in a big-endian or small-endian format, you can convert it manually. For example, if you receive a 32-bit integer (usually a big endian) from the network and the local one is a little endian, you need to convert it into a little endian before use.

A common approach is to use bit operations or union to convert:

 uint32_t ntoh_custom(uint32_t val) {
    return ((val >> 24) & 0x000000FF) |
           ((val >> 8) & 0x0000FF00) |
           ((val << 8) & 0x00FF0000) |
           ((val << 24) & 0xFF000000);
}

This approach is suitable for all platforms, but it is not necessarily optimal for efficiency. In actual development, it is recommended to use standard libraries or system APIs, such as functions such as ntohl() and htonl() , which have been widely tested and optimized.

Use standard libraries or cross-platform tools

The C standard library itself does not directly provide functions for endianness conversion, but you can rely on some cross-platform libraries, such as Boost or absl (Google's Abseil library), which all provide convenient interfaces:

• Boost.Endian : Provides a portable endian conversion template.
• absl::Endian : Google Abseil provides efficient conversion functions that support data types of various sizes.

If you don't want to introduce third-party libraries, you can also encapsulate a set of macros or functions yourself and automatically choose the appropriate implementation method according to the compiler and platform.

Common practices include:

• Use predefined macros to determine the CPU architecture (such as __BYTE_ORDER__ )
• Include corresponding transformation logic for different situations
• For constant data, conversion can be completed during compilation

This ensures the portability and maintainability of the code.

Be extra careful when handling structures or buffers

When you read an entire structure from a file or network, direct memcpy may cause data errors due to endianness issues. Especially when the structure contains integer fields, it must be converted one by one.

The recommended approach is:

• Read raw data by bytes to the buffer
• Access each field with a pointer and convert it manually
• Don't directly reinterpret_cast external data into a structure pointer

For example:

 uint32_t* data = reinterpret_cast<uint32_t*>(buffer offset);
value = ntoh_custom(*data);

Although this method is a little troublesome, it can avoid many hidden bugs.

Basically that's it. Byte order processing is not complicated but details are easy to ignore, especially in multi-platform development. A little carelessness will lead to compatibility issues. As long as you make a conversion in the data input and output links, most traps can be effectively avoided.

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